Interfacially-Adsorbed Particles Enhance the Self-Propulsion of Oil Droplets in Aqueous Surfactant

We have demonstrated that adsorption of silica nanoparticles at the interface of a solubilizing oil droplet in surfactant solution can significantly accelerate the droplets’ self-propulsion speed. Using fluorescent particle visualization, we correlated the degree of particle surface coverage on bromodecane droplets to the droplet speed in TX surfactant. Slowest speeds were found at the lowest and highest surface coverages and the fastest speeds were achieved at intermediate surface coverages of about 40%. The particle-assisted propulsion acceleration was further demonstrated in nonionic, anionic, and cationic surfactants and a range of oils with varying solubilization rates. We propose that particles at the droplet interface hinder solubilization by displacing oil-water interfacial area, providing asymmetry in the distribution of oil-filled micelles along the droplet surface and accelerating Marangoni flow. We describe a fluid-mechanical model to rationalize the effect of the particles by considering the effect of a non-symmetrical distribution of solubilized oil at the droplet surface. Approaches by which to modulate the distribution of solubilization across droplet interfaces may provide a facile route to tuning active colloid speeds and dynamics. <br>

Influence of surface roughness on the light transmission through the boundaries of luminescent materials in radiation detectors-=SUP=-*-=/SUP=-

The optical transfer properties of an imaging system are affected by the performance of the discrete cascaded system stages that transfer efficiently the optical signal. Apart from the contribution of each component to the overall optical propagation, crucial role also plays the intermediate surface conditions. Surface roughness is characterized by irregularities with respect with the ideal smooth form. The degree of roughness has an influence on the surface behavior affecting correspondingly the overall enhancement of system's optical performance. In this manuscript, the angle dependent effect of surface roughness on phosphor . optical materials configuration is provided taking into account eight luminescent materials (CsI, Y3Al5O12, Y2O3, Bi4Ge3O12, CaWO4, ZnS, Lu2O3 and Gd2O2S) and three optical materials (InGaAs, ITO and SiO2). Results showed that higher transmission optical properties exhibited the: (i) CsI-InGaAs combination, (ii) ZnS-ITO and (iii) ZnS-SiO2 combination. The transmission factor was also quantitatively affected by increasing the surface roughness values and by decreasing the incident polar angles. Keywords: luminescent materials, optical sensors, surface roughness

Interfacially-Adsorbed Particles Enhance the Self-Propulsion of Oil Droplets in Aqueous Surfactant

We have demonstrated that adsorption of silica nanoparticles at the interface of a solubilizing oil droplet in surfactant solution can significantly accelerate the droplets’ self-propulsion speed. Using fluorescent particle visualization, we correlated the degree of particle surface coverage on bromodecane droplets to the droplet speed in TX surfactant. Slowest speeds were found at the lowest and highest surface coverages and the fastest speeds were achieved at intermediate surface coverages of about 40%. The particle-assisted propulsion acceleration was further demonstrated in nonionic, anionic, and cationic surfactants and a range of oils with varying solubilization rates. We propose that particles at the droplet interface hinder solubilization by displacing oil-water interfacial area, providing asymmetry in the distribution of oil-filled micelles along the droplet surface and accelerating Marangoni flow. We describe a fluid-mechanical model to rationalize the effect of the particles by considering the effect of a non-symmetrical distribution of solubilized oil at the droplet surface. Approaches by which to modulate the distribution of solubilization across droplet interfaces may provide a facile route to tuning active colloid speeds and dynamics. <br>

Interfacially-Adsorbed Particles Enhance the Self-Propulsion of Oil Droplets in Aqueous Surfactant

We have demonstrated that adsorption of silica nanoparticles at the interface of a solubilizing oil droplet in surfactant solution can significantly accelerate the droplets’ self-propulsion speed. Using fluorescent particle visualization, we correlated the degree of particle surface coverage on bromodecane droplets to the droplet speed in TX surfactant. Slowest speeds were found at the lowest and highest surface coverages and the fastest speeds were achieved at intermediate surface coverages of about 40%. The particle-assisted propulsion acceleration was further demonstrated in nonionic, anionic, and cationic surfactants and a range of oils with varying solubilization rates. We propose that particles at the droplet interface hinder solubilization by displacing oil-water interfacial area, providing asymmetry in the distribution of oil-filled micelles along the droplet surface and accelerating Marangoni flow. We describe a fluid-mechanical model to rationalize the effect of the particles by considering the effect of a non-symmetrical distribution of solubilized oil at the droplet surface. Approaches by which to modulate the distribution of solubilization across droplet interfaces may provide a facile route to tuning active colloid speeds and dynamics. <br>

Interfacial Hydroxyl Promotes the Reduction of 4 Nitrophenol by Ag-Based Catalysts Confined in Dendritic Mesoporous Silica Nanospheres

Surface states—the electronic states emerging as a solid material terminates at a surface—are usually vulnerable to contaminations and defects. This fundamental limitation has prohibited systematic studies of the potential role of surface states in surface reactions and catalysis, especially in more realistic environments. We use the selective reduction of 4-Nitrophenol on silver-covered dendritic mesoporous silica nanospheres (DMSNs) as a prototype example, and show that the dynamic intermediate surface states (DISS) spatially formed by spin orbital coupling (SOC) in singly hydrated hydroxyl complex can significantly enhance the adsorption energy of both 4-Nitrophenol and BH4- anions, by promoting different directions of static electron transfer. The concept of DISS as an electron bath may lead to new design principles beyond the conventional d-band theory of heterogeneous catalysis.

Interfacial Hydroxyl Promotes the Reduction of 4 Nitrophenol by Ag-Based Catalysts Confined in Dendritic Mesoporous Silica Nanospheres

Surface states—the electronic states emerging as a solid material terminates at a surface—are usually vulnerable to contaminations and defects. This fundamental limitation has prohibited systematic studies of the potential role of surface states in surface reactions and catalysis, especially in more realistic environments. We use the selective reduction of 4-Nitrophenol on silver-covered dendritic mesoporous silica nanospheres (DMSNs) as a prototype example, and show that the dynamic intermediate surface states (DISS) spatially formed by spin orbital coupling (SOC) in singly hydrated hydroxyl complex can significantly enhance the adsorption energy of both 4-Nitrophenol and BH4- anions, by promoting different directions of static electron transfer. The concept of DISS as an electron bath may lead to new design principles beyond the conventional d-band theory of heterogeneous catalysis.

Relationships between Surface Properties and Snow Adhesion and Its Shedding Mechanisms

Understanding the mechanisms of snow adhesion to surfaces and its subsequent shedding provides means to search for active and passive methods to mitigate the issues caused by snow accumulation on surfaces. Here, a novel setup is presented to measure the adhesion strength of snow to various surfaces without altering its properties (i.e., liquid water content (LWC) and/or density) during the measurements and to study snow shedding mechanisms. In this setup, a sensor is utilized to ensure constant temperature and liquid water content of snow on test substrates, unlike inclined or centrifugal snow adhesion testing. A snow gun consisting of an internal mixing chamber and ball valves for adjusting air and water flow is designed to form snow with controlled LWC inside a walk-in freezing room with controlled temperatures. We report that snow adheres to surfaces strongly when the LWC is around 20%. We also show that on smooth (i.e., RMS roughness of less than 7.17 μm) and very rough (i.e., RMS roughness of greater than 308.33 μm) surfaces, snow experiences minimal contact with the surface, resulting in low adhesion strength of snow. At the intermediate surface roughness (i.e., RMS of 50 μm with a surface temperature of 0 °C, the contact area between the snow and the surface increases, leading to increased adhesion strength of snow to the substrate. It is also found that an increase in the polar surface energy significantly increases the adhesion strength of wet snow while adhesion strength decreases with an increase in dispersive surface energy. Finally, we show that during shedding, snow experiences complete sliding, compression, or a combination of the two behaviors depending on surface temperature and LWC of the snow. The results of this study suggest pathways for designing surfaces that might reduce snow adhesion strength and facilitate its shedding.

NLTE spectral analysis of the intermediate helium-rich subdwarf B star CPD−20°1123

ABSTRACT Subdwarf B (sdB) stars are core helium-burning stars with stratified atmospheres. Their atmospheres are dominated by hydrogen (H) while the helium (He) and metal abundances are shaped by an interplay of gravitational settling and radiative levitation. However, a small fraction of these show spectra dominated by He i absorption lines. In between these groups of He-deficient and extreme He-rich sdBs, some are found to have intermediate surface He abundances. These objects are proposed to be young ‘normal’ (He-deficient) sdBs for which the dynamical stratification of the atmosphere is still ongoing. We present an analysis of the optical spectrum of such an intermediate He-rich sdB, namely CPD−20°1123, by means of non-local thermodynamic equilibrium (NLTE) stellar atmosphere models. It has a He-to-H number ratio of He/H = 0.13 ± 0.05 and its effective temperature of $\mbox{$T_\mathrm{eff}$} = 25\, 500 \pm 1000 \, \mathrm{K}$ together with a surface gravity of $\log \, (g$ / cm s−2) = 5.3 ± 0.3 places the star close to the high-temperature edge until which it may be justified to use LTE model atmospheres. This work states a test of the Tübingen NLTE Model Atmosphere Package for this temperature regime. We present the first application of revised, elaborated model atoms of low ionization stages of light metals usable with this atmosphere code.